linux-kernel - Re: [PATCH] x86/asm/entry/64: Clean up entry

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Message-ID: <559AB49F.3070008@oracle.com>
Date:	Mon, 06 Jul 2015 13:02:23 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Denys Vlasenko <dvlasenk@...hat.com>, linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/asm/entry/64: Clean up entry_64.S

On 07/06/2015 12:43 PM, Ingo Molnar wrote:
> 
> * Sasha Levin <sasha.levin@...cle.com> wrote:
> 
>> On 07/06/2015 12:23 PM, Ingo Molnar wrote:
>>>
>>> * Sasha Levin <sasha.levin@...cle.com> wrote:
>>>
>>>> On 07/06/2015 12:07 PM, Ingo Molnar wrote:
>>>>>
>>>>> * Sasha Levin <sasha.levin@...cle.com> wrote:
>>>>>
>>>>>> Hey Ingo,
>>>>>>
>>>>>> I've started seeing the fuzzer hitting the BUG() at arch/x86/kernel/nmi.c:533. git
>>>>>> blame pointed to this patch. I know that you didn't see any changes in the compiled
>>>>>> file in your testcase, but I do see changes in mine.
>>>>>
>>>>> Hm, weird - could you send me your .config please?
>>>>
>>>> Attached.
>>>
>>> It's still weird: I copied your config to 4d7321381e5c and made 'make oldconfig' - 
>>> and it asked a couple of questions, which suggests that your config does not come 
>>> from 4d7321381e5c?
>>
>> Right, sorry, this is my base config for -next. I just did 'yes "" | make oldconfig'
>> for the build test.
>>
>> I've attached it.
>>
>>> Furthermore, building 4d7321381e5c and 4d7321381e5c^1 gives me:
>>>
>>>   # arch/x86/entry/entry_64.o:
>>>
>>>    text    data     bss     dec     hex filename
>>>   11530       0       0   11530    2d0a entry_64.o.before
>>>   11530       0       0   11530    2d0a entry_64.o.after
>>>
>>> md5:
>>>    1430e793250d5d8572bc2df2997d3929  entry_64.o.before.asm
>>>    1430e793250d5d8572bc2df2997d3929  entry_64.o.after.asm
>>>
>>> i.e. I have trouble reproducing the discrepancy you are seeing. (I also tried 
>>> allmodconfig/allyesconfig again for good measure - no luck.)
>>
>> With allyesconfig I don't actually see a change. Only with the config I've attached.
> 
> So I still cannot reproduce it even with your latest config:
> 
>   # arch/x86/entry/entry_64.o:
> 
>    text    data     bss     dec     hex filename
>   11530       0       0   11530    2d0a entry_64.o.before
>   11530       0       0   11530    2d0a entry_64.o.after
> 
> md5:
>    1430e793250d5d8572bc2df2997d3929  entry_64.o.before.asm
>    1430e793250d5d8572bc2df2997d3929  entry_64.o.after.asm
> 
> but I saw this during the build:
> 
>   scripts/Makefile.kasan:23: CONFIG_KASAN: compiler does not support all options. Trying minimal configuration
> 
> is your KASAN build more fully enabled, and does the problem reproduce with 
> CONFIG_KASAN turned off?

KASAN was fully enabled, but this reproduces with CONFIG_KASAN turned off as well.

I also thought that it might be because I'm using gcc6, but going back to 4.7.2
produced the same difference.


Thanks,
Sasha

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